If they do overland exploration well, I'll be happy with it. Until then it isn't a selling point for me. I'd rather a geographically correct world with fast travel between points, instead anyway. The best solution is the one Nottheking came up with.
I dont really like oblivion that much, but I've been quite happy with what modders have made in the empty spaces. I'm talking about you, http://www.oblivionmodwiki.com/index.php/Unique_Landscapes.
That kind of thing really has the potential to greatly enhance the overworld exploration aspect of the game. Mix that with something like what I linked earlier involving http://www.youtube.com/watch?v=CIyx23OY8Nk&feature=related
Now all that has to be done is getting a little creative with city interiors (or exteriors if theyre http://www.tesnexus.com/downloads/file.php?id=16360 prior to modifications) ...Also Levitate
If you think about it this can lead to a lot more spatial interactivity, OK, so you dont have a button that makes you stick to a wall and go up and up like AC; or even the acrobatics of Mirrors Edge, but its still spatial interaction, as opposed to just walking over flat land.
I greatly enjoyed trying to roof hop around balmora, just becuase you dont have a tool that has big shiny instructions on it saying PRESS X TO CLIMB STUFF! doesnt mean you cant get creative. Though the earlier point was made that there is very little in the way of vertical growth in Oblivions cities, which is totally possible to be changed, add some cliff meshes morph some landscape, use those rope arrows; and, my god! look at me, I'm spiderman!
This is the beauty of TES they take the Gamebryo engine dabble in multiple fields to give access to the basics of each type of interaction, then let the community go wild taking it in whatever direction they want.
Streamlining the game (from a design and programming standpoint) to run as well as AC doing only a few things like creating massive cities, most likely culls a lot of the stub mechanics involved with Bethesdas fledgling attempts at various other mechanics, radiant AI, as much as people bashed it is there for people to expand to their hearts content, they just dont, people want it given to them which is a shame because you cant just give and give and give. Anyway the RadiantAI is potentially infinitely better than what they advertised to us. All that is required is a little leg work on our part. This is the difference between simply consuming a game and using it to its full potential.